I just don't think you need be concerned with Orthene. I have used it for years and have never experienced it harming anything other than what I am trying to eliminate. Heck, I use it on many of my tropical plants, orchids included, and would not hesitate to use it on any of my tropical plants.
The nice thing is that it only takes a very small amount of dust to do the ants in. If you fear using it as a dust, just make up a solution and use it as a light drench. It works either way.
